Disposal of oil spill at sea

ABSTRACT

METHOD FOR DISPOSING OF OIL SPILLED AT SEA BY FIRST BURNING THE OIL AND THEREAFTER APPLYING AN INORGANIC SINKING AGENT. THE SINKING AGENT PARTICLES, LESS THAN 50 MM. IN SIZE, ARE DISPERSED OVER THE BURNING OIL AND BECOME COATED WITH THE OIL RESIDUE WHICH IS ABSORBED ONTO THE PARTICLES AS THEY SINK. THE SINKING AGENT PARTICLES MAY BE SAND, GRAVEL, CHALK, GYPSUM, SLAG OF HEAVY MATERIALS LIKE IRON ORE, AND THE LIKE.

United States Patent 3,749,667 DISPOSAL OF OIL SPILL AT SEA Olle B. Lindstrom, Lorensviksvagen 14, Taby, Sweden No Drawing. Filed Nov. 18, 1971, Ser. No. 200,162 Claims priority, application Sweden, July 9, 1971, 8,899/ 71 Int. Cl. E02b 15/04 US. Cl. 210-36 8 Claims ABSTRACT OF THE DISCLOSURE Method for disposing of oil spilled at sea by first burning the oil and thereafter applying an inorganic sinking agent. The sinking agent particles, less than 50 mm. in size, are dispersed over the burning oil and become coated with the oil residue which is absorbed onto the particles as they sink. The sinking agent particles may be sand, gravel, chalk, gypsum, slag of heavy materials like iron ore, and the like.

This invention relates to the disposal of oil spills at sea.

Oil spills from ships is a considerable environmental hazard and a number of methods have therefore been developed to get rid of oil spill at sea. These methods are, for instance, (1) limitation of the spread-out of the oil by means of booms, air barriers, or so-called monolayer forming agents, (2) mechanical uptake, possibly by means of absorbing materials and gelling or gelatinizifig agents, (3) emulsification of the oil, (4) sinking, and (5) combustion. To these methods could be added more speculative methods such as biological decomposition by means of special bacteria, etc.

These methods exhibit drawbacks of different kinds. Very large quantities of emulsifiers are required for disposal by emulsification and frequently these emulsifiers or dispersing agents cause effects on the environment that are more harmful than the oil. When the oil is subjected to sinking, it is necessary to treat the sand or chalk which is used for this purpose by means of silicones, sodium stearate, or like materials to make the sinking agents oleophilic. Combustion is, of course, a suitable method in principle but it gives incomplete destruction even when additional or auxiliary agents like wicks, secondary flames, oxygen, and the like are used.

It is an object of the present invention to provide a novel method for disposing of an oil spill at sea through use of a combination of known principles, which gives a surprisingly simple and efiicient solution to this problem. The method is characterized in that a sinking agent in the form of small particles is applied to the oil layer while this is in burning condition, or immediately thereafter. It is of advantage in accordance with the present invention to maintain combustion by means of oxygen or mixtures of oxygen and air. When the spilled oil is difficult to burn, it may also be necessary to apply additional solid or liquid fuels such, for example, as naphtha.

It has been found that the sinking agent particles when applied under these conditions become covered with products of a cokey and/or tarry consistency. These products have a strong absorbent capacity for non-reacted components in the oil and for combustion products which become bound to this cokey layer. In this way, the oil itself is producing an absorption agent which, thanks to the sinking agent, is disposed on the sea bottom. In general, it is not necessary to carry out a special treatment of the sinking agent to make it more hydrophobic since this will occur when the sinking agent comes into contact with the burning oil phase. The amount of contaminating materials which are disposed on the sea bottom will be less than with sinking alone since a large part of the oil will burn to gaseous reaction products.

Sinking or burning, each used alone, are not a suitable way for the disposal of an oil spill at sea. The combination of these two methods gives, as has been described above, apparently new effects which exceed the sum of what the two methods can produce each on its own. Of course, it is frequently of advantage to combine the method according to the invention with means to prevent the spreading of the oil, for instance, booms.

In practicing the invention, one has to be governed by the type and quantity of oil let out or spilled. Since the characteristic feature for the method is the combination of first burning and then sinkinng the residue, it is frequently of advantage to supply the sinking agent during the'burning operation or promptly after burning has stopped. However, it is not necessary that the sinking agent be applied during the whole combustion process. It is frequently recommendable to wait and apply the sinking agent at or near the end of the combustion to reduce the quantity of sunk material to a minimum. This is particularly important when the life at the sea bottom is sensitive. At the same time, however, one wants to get a high degree of coating on the sinking material particles and take advantage of the absorption capacity of the cokey material in the residue. Under other circumstances, when one desires the disposal from the surface to be as fast as possible, it is recommendable to apply the sinking agent already from the beginning of the combustion. It has been found to be particularly advantageous to apply the sinking agent on the oil spill in a stream of air which can be enriched with oxygen or also be pure oxygen. In this way, the sinking agent can be propelled over a long distance from the sanitation ship and at the same time support the combustion of the oil. The sinking agent may also be thrown on the oil slick by means of mechanical throwing equipment, such as rotating shovel wheels and the like. In this case, the combustion will be stimulated by the stream of air which is simultaneously generated.

The etficiency of the method according to the present method has been demonstrated by the following example from a laboratory test. 150 g. of oil was arranged in a vessel with streaming water, the oil being maintained within a ring of metal with 15 cm. diameter, which was kept at the surface by means of a cork. The oil was put in first and caused to begin burning, and thereafter 250 g. of sand with a particle diameter of 1 mm. was applied during the combustion process. The oil was sunk and the quantity of oil thus sunk amounted to about g., or over 70% of the oil originally present.

In a similar test with additional oxygen supply, the quantity of oil sunk was reduced to 60 g., thanks to the added combustion. The sunk material in both tests had a cokey consistency.

For comparison, tests using only organic substances which. in the past, have been used by others for stimulating combustion of the oil spill, such as wood chips, straw, naphtha (to support the oil fire), polystyrene foam, etc., produced large quantities of thick and smeary materials which remained on the surface. In these cases, the combustion had to be supplemented in a known manner as by mechanical means. Regardless of the extent of supplementation of combustion, the surface was not cleared as a result of burning alone.

As sinking agents, inorganic materials must be used which have the property of becoming coated with the floating oil residue and a density when saturated with the residue greater than that of water. Materials such as native, crushed, or ground inorganic materials like g c alk, gypsum, slag of heavy minerals like iron ore and the like, are used to advantage. The sinking agent must be heavier than water, even when coated with the oil residue, and should have an average particle diameter of generally within the limits 0.1-50 mm. with the best results being obtained where the particle has a maximum dimension between about 0.5 and 2 mm. The optimum particle size is governed to a large extent by the thickness, viscosity, and other characteristics of the oil spill with thin layers of low viscosity oil requiring the use of smaller szed partcles.

The partcle size and dosage of the sinking agent is adjusted so that the sinking agent remains on the surface of the burning oil layer for a time sufficient to produce cokey and tarry products on the surfaces of the sinking agent particles. In practice, it should be recognized that some of the sinking agent particles will fall through the oil layer so rapidly that only minor quantities of the oil become absorbed on those particles. If the application is improper, it may be necessary to use a considerable overdose of sinking agent, perhaps -200 times more or above that which would be necessary on theoretical grounds, to sink the total oil quantity in question. However, by applying the sinking agent of optimum particle size after the oil layer has been burning sufiiciently long to increase the temperature and reduce the viscosity of the oil layer, the oil residue has new properties which enhance the bond between the sinking agent and the residue in the oil layer.

In addition to applying the sinking agent while the fire is burning, I have found that the sinking agent can also be applied immediately after the fire has ceased but while the oil residue still has the properties and condition of burning oil, which is important for causing the residue to become coated on and/or absorbed on the surface of the particles of sinking agent. The important point is that the sinking agent should be applied before the oil layer has essentially lost the properties which give a good bond to the sinking agent.

The temperature in the oil layer and its viscosity are of great importance as well as the presence in the oil layer of intermediate combustion and pyrolysis products. These parameters vary with the kind of oil, the thickness of the oil layer, and the degree of combustion. It has therefore been found useful to determine, for every special case of oil disposal, in a small scale experiment with the actual type oil, layer thickness, etc., how much time is available after the first has ceased until the character of the oil layer from a sinking point of view being in burning condition has essentially been lost. Sinking agents are applied at different times after the fire has ceased. When the character of the oil layer has disappeared, it is not possible to sink the layer etficiently except by using extremely large quantities of sinking agent since the sinking agent will attach itself loosely on the oil layer without being taken up by the same. Practical experiments have shown that this period of time immediately after the fire has ceased may amount to a few seconds in cases with thin oils and thin layers, whereas in other cases, the time may be several tens of minutes up to 1 hour, and in extreme cases, more.

When the sinking agent is applied to the oil layer immediately while the fire is burning, the products of combustion appear to provide a conditioning of the surface of the sinking agent which enhances the bond between the sinking agent surfaces and the oil residue. It is, however, not entirely to be excluded that a similar action may be produced by gas given off from the oil layer which has just ceased burning. Conditioning of the sinking agent is, however, possibly not an entirely exhaustive explanation of the reasons for the surprisingly good effect of the combination method. One has also to consider the condition of the oil layer itself as it is developed during the combustion and which apparently may remain some time after the fire has visually ceased.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and intended to be covered by Letters Patent is:

1. A process for clearing up from the water surface an oil spill at sea by causing combustion of the burned oil to thereby produce a cokey and tarry floating residue, thereafter sinking the floating residue by applying a sinking agent to the residue surface, said sinking agent comprising particles of an inorganic material having the property of becoming coated with floating residue and a density when saturated with said residue greater than that of water, said particles having a size to sink gradually through said residue after becoming coated therewith.

2. The process of claim 1 wherein said particles have an average size between 0.1 to 50 mm.

3. The process of claim 2 wherein the sinking agent is applied while the oil is in a burning condition.

4. The process of claim 2 wherein the sinking agent is applied after the fire has ceased but while the residue has the properties and condition of burning oil which effect a good bond between the sinking agent and oil residue.

5. The process of claim 4 wherein said particles are selected from the group consisting of sand, gravel, chalk, gypsum, and a slag of heavy minerals.

6. The process of claim 1 wherein said particles have a maximum dimension between about 0.5 and 2 mm. and are applied to the surface of the burning oil spill in a stream of air.

7. The process of claim 6 wherein the air stream is enriched with oxygen to enhance the combustion process.

8. The process of claim 6 wherein said particles are selected from the group consisting of sand, gravel, chalk, gypsum, and a slag of heavy minerals.

References Cited UNITED STATES PATENTS 2,464,204 3/1949 Baker 210-40 X 3,556,698 l/1971 Tully et al. 2lO 40 X 3,562,153 2/1971 Tully et a1. 21036 OTHER REFERENCES Arthur D. Little, Inc., Combating Pollution Created by Oil Spills, vol. 1, June 30, 1969, Ad 696,635, pp. 72, 73.

SAMIH N. ZAHARNA, Primary Examiner I. CINTINS, Assistant Examiner US. Cl. X.R.

21040, 63, DIG. 21; 431-2 

